As the measures for protecting a windmill turbine blade or an overall windmill device from a lightning striking upon the windmill blade, for example, a Patent Document 1 (PCT-WO2004/111686A1) or a Patent Document 2 (PCT-WO2005/026538A1) proposes a lightning protection device comprising a lightning receptor attached to the outer surface of a blade, from which a lightning current caused by a lightning striking to the receptor is led to the ground through a conductor extended through the inside of the blade, a rotor head, a main shaft, a tower and the like in the body part of the windmill device.
In the technology disclosed in Patent Document 1, lightning receptors are arranged at several positions at the outer surface of a windmill blade along the lengthwise direction of the blade from the tip end part thereof, and lightening currents from the receptors are discharged to the ground through leas wires led through the inside of the blade and the windmill body.
In the technology disclosed in Patent Document 2, lightning receptors are exposed at the outer surfaces of the belly side shell and the back side shell of the blade, as viewed in a predetermined section of the blade so as to allow a lightning to strike thereto, and the receptors are fixed respectively at the rear surface of the belly side shell and the back side shell by means of screws while lead wires from the receptors are connected to a down conductor.
However, although the technology disclosed Patent Document 1 concerns the configuration that lightening currents from the lightning receptors which are arranged at several positions along the lengthwise direction of the blade from the tip end thereof, are discharged to the ground through the lead wires led in the inside of the blade and the windmill body, and although the technology disclosed in Patent Document 2 concerns the configuration that the lightning receptors are exposed at the belly side shell and the back side shell of the blade so as to allow a lightning to strike thereto while the receptors are fixed respectively at the rear surfaces of the belly side shell and the back side shell by means of screws, both Patent Documents fail to disclose effective measures for assembling a receptor to the tip end part of the blade having a smaller airfoil profile, a countermeasure against a pressure increase induced in the inside of the blade upon striking of a lightning to the blade, and the like.